By AccuWeather Meteorologist
Published Feb 19, 2023 12:03 PM EST | Updated Feb 20, 2023 6:30 PM EST
AccuWeather meteorologists say an active weather pattern across the Western U.S. this week can pull in brisk, Arctic air and help produce areas of heavy mountain snow. In the upper levels of the atmosphere, the jet stream will begin to plunge southward during the first half of the week, which will help usher in a large storm to the Northwest.
Winter storm warnings were in place across the Pacific Northwest and parts of the Rockies Monday, while winter storm watches extended from parts of Wyoming to western Wisconsin.
Conditions across the West started off somewhat mild for many locations on Monday compared to the harsh cold that will arrive by midweek.
A fast-moving clipper storm and its associated frontal boundary will swing through parts of the northern Rockies into the Upper Midwest and Great Lakes region from Monday into Tuesday. As this feature traverses across the northern tier of the Western and Central states, it will begin to pull chilly, Arctic air southward into the United States from Alberta and Saskatchewan.
Nature will start to give the West hints of what is to come, lowering temperatures by a few degrees on Tuesday across parts of Washington, Oregon, Idaho and Montana.
Another storm will follow closely behind the clipper storm, arriving in full force Tuesday in the Northwest. All eyes will be on this segment as it is expected to track southward and deepen as it brings cooler air, snow and gusty winds and as far south as the Four Corners.
Disruptive high winds could develop across locations such as Marias Pass, Livingston, Montana, southeastern Wyoming and portions of the Front Range, where winds can gust as high as 80 mph, according to AccuWeather Meteorologist Brandon Buckingham.
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By Tuesday night and Wednesday, the strongest winds will shift southward, impacting many of the high deserts and mountainous regions of New Mexico, Arizona and Southern California. Gusty winds will even extend all the way to the coast, impacting the San Diego metro area with gusts as high as 50 mph.
Forecasters warn that strong winds across these areas on Monday and Tuesday can lead to travel slowdowns along area roadways and interstates, such as interstates 25, 70, and 80 in Wyoming, Utah and Colorado. The strongest winds are likely to occur in portions of New Mexico and Arizona, where AccuWeather Local StormMax™ gusts near 100 mph are possible.
As the gusty winds expand southward from Montana to Colorado, the blustery conditions will be accompanied by periods of snow across the ranges of the northern Rockies and, eventually, the Colorado Rockies.
Occasional snowfall will focus across the higher terrain of the Washington Cascades and the Rockies in Idaho, Montana and northern Wyoming into Monday night. By Tuesday, periods of snow will reach southward into parts of Oregon, Northern and Central California, Nevada, Utah and Colorado while also persisting in the northern Rockies.
Several areas had already recorded 7 or more inches of snow as of Monday afternoon, including Battle Lake and Gillette, Wyoming. To the north in Montana, 5 inches of snow was observed near Hardin on Monday afternoon.
In Salt Lake City, rain showers are expected to shift to snow throughout Tuesday. Overnight on Tuesday, conditions will gradually transition over to periods of snow, which can persist through Wednesday and total 6-10 inches. Snow levels will also lower on Tuesday in places like Reno, Nevada, dropping to 5,200 feet by the afternoon.
Stark temperature drops across interior West by midweek
As the storm plunges southward into parts of the Southwest late Tuesday into Wednesday, a dramatic temperature shift will occur from Montana to Utah and Colorado as brisk air is pulled from Canada.
"Temperature readings can drop quickly, likely falling between 20-40 degrees over 24 hours for most locations," said Buckingham.
In Billings, Montana, high temperatures on Wednesday may only reach 4 degrees below zero F, a noticeable difference from the expected Tuesday daytime high of 35 F. Similarly, in Casper, Wyoming, daytime highs from Tuesday to Wednesday can shift from 41 F to 1 F, respectively.
Other notable shifts in temperature from Tuesday to Wednesday can occur in Denver and Salt Lake City. Salt Lake City could observe a 24-hour temperature change of 17 F, while Denver can drop to around 29 F heading into midweek.
In the highest elevations of the Cascade Range, northern Rockies and Colorado Rockies, snowfall amounts can total up to 18-24 inches from Sunday to Wednesday with the AccuWeather Local StormMax™ of 60 inches.
Snow will continue to spread southward along the Sierra Nevada as well as mountains in Arizona and New Mexico through Wednesday night. In Arizona, the highest snowfall accumulations ranging from 6-12 inches are likely to dominate portions of the Kaibab Plateau, White Mountains and Mogollon Rim. Similarly, the highest peaks of the Sierra Nevada could observe amounts ranging from 6-12 inches from Tuesday to Wednesday.
Snow to dip to low levels in California
From Wednesday to Thursday, snow levels may dip to close to 1,500 feet around San Francisco.
"This means that not only may some of the hills in the region receive a coating of snow, but snowflakes could make a rare appearance at some lower elevations," AccuWeather Senior Meteorologist Dave Houk said.
Since snow levels will dip to around 2,000 feet in Southern California, slippery road conditions are likely over the passes north and east of Los Angeles from Wednesday night to Friday evening.
A period of heavy snow prior to the end of the week could bring several inches of snow over the Grapevine, ridges and peaks in the region, and could cause Interstate 5 to close for a time over the higher elevations.
Enough rain may fall at lower elevations in coastal Southern California from Thursday to Friday evening to make for slick roads as well as create incidents of flash flooding and debris flows. A general 1-4 inches of rain is likely with locally higher amounts over the lower south- and west-facing mountainsides.
Residents within the zone of the storm's impacts this week could face a variety of hazards ranging from blowing snow, wind-driven rain, difficult travel and road closures. Gusty winds could also raise the risk of vehicle blowovers, particularly with high-profile vehicles.
As this feature gradually tracks east of the Rocky Mountains from mid-to late week, it will continue to spread a swath of snow and the threat for ice from the Great Lakes to areas of the Northeast.
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